Fuel systems for internal combustion engines and gas turbines



May 20, 1958 D. e. BOOTH 2,835,323

FUEL SYSTEMS FOR INTERNAL COMBUSTION ENGINES AND GAS TURBINES Filed Oct.14, 1954 2 Sheets-Sheet 1 CONTROL UNIT ENGINE CZMWZS, uoucLns QERHQRDBOOTH.

Filed Oct. 14, 1954 May 20, 1958 o. G. BOOT H I 2,835,323

FUEL SYSTEMS FOR INTERNAL COMBUSTION ENGINES AND GAS TURBINES 2Sheets-Sheet 2 DOUGLAS .GERHARD BOOTH.

United rates Patent (3 FUEL srsrsrus son tarnish COMBUSTION Enemies ANDGAS ronnmns Douglas Gerhard Booth, lllford, England, assignor to ThePlessey' {Tompany Limited, lllford, England, a British companyApplication Uctoher 14, 1954, Serial No. 462,284

2 Claims. (Cl. 158-363) This invention relates to a fuel system forinternal combustion engines and gas turbines, more particularly aircraftengines.

In an aircraft engine fuel system, it is sometimes desirable to savespace, weight and to effect an economy, to use simple fixed displacementpumps to supply the engine with fuel. These pumps operate satisfactorilyat low altitudes but at high altitudes, where the engine fuelrequirements become low and it is necessary to by-pass a largeproportion of the pump delivery back to the inlet, a considerable amountof energy is put into the small amount of fuel required by the engine.This causes a rise in temperature of the fuel which in extreme cases cancause failure of the pump or control system.

An object of this invention is to reduce this rise in temperature byusing two or more fixed displacement pumps.

According to this invention, a fuel system has two or more pumps forsupplying liquid fuel to an engine in excess of maximtun requirements,the excess fuel being by-passed back to the low pressure side of thesystem, and a servo-valve means operatively connected with the deliveryside of one or more of the pumps and the low pressure side, enabling thedelivery from said pump or pumps to be separately lay-passed at lowpressure when the flow in the by-pass exceeds a pre-determined value,whereby one or more pumps is unloaded.

A feature of the invention is that a common flow responsive valve isprovided irrespective of the number of displacement pumps and each saidpump has a separated servo-operated valve and non-return valve, thus forexample in the case of three or more pumps, the now to low pressure fromthe second, third and so on pumps, operates in sequence. In the casewhere there are three pumps, if the demand is such that one pump is notrequired, it by-passes liquid fuel back to low pressure by the operationof its associated servo-valve means. If the demand for liquid fuel isstill insufiicient for two pumps, then the supply from the second pumpis bypassed to low pressure through actuation of the secondservo-operated means, thereby leaving one pump in operation.

The invention will now be described with reference to the accompanyingdrawings in which- Fig. l is a block diagram of one embodiment using twopumps, and

Fig. 2 is a block diagram of a system using three pumps.

Referring to Fig. l of the drawings:

A tanl: 1 containing liquid fuel. is connected by a conduit 2 to twoparallel passages 3, 4. Each passage 3 and 4 contains gear pumps 5 and 6for supplying pressurized liquid fuel through nonreturn valves 7, 8 to acontrol unit 9 of a known type.

The control unit 9 meters the correct amount of liquid fuel to an engineiltl and excess fuel is by-passed through conduit 11 containing a fiowresponsive valve 12 back ice 2 to the low pressure side of conduit 2.The flow responsive valve 12 comprises a sleeve in which is formed anorifice 12a and provided with a spring 12b. A passage 11a forms acontinuation of conduit 11 when the flow responsive valve 12 is in thefully closed position.

A branch passage 13 leading from the passageway 3 of the pump 5 isconnected to a servo-operated throttle valve 14 whereby pressurised fuelfrom the delivery side 15 of the pump 55 is passed to low pressure ashereinafter set forth.

A conduit 16 leading from the by-pass 11 to a servovalve cylinder 17contains a restrictor orifice 18.

A port 19in the flow responsive valve 12 is connected by a passage 20 tothe servo-valve cylinder 17 to adjust the throttle valve 14 in thepassage 13.

The operation of the system will now be described as applied to anaircraft.

At low altitudes the fuel flow required by the engine 10 is high and theflow in the by-pass 11 will be below a pre-determined value. The flowresponsive valve 12 will be in a position that will leave the port 19open and the servo chamber 17 at low pressure. The servo valve 14 willbe fully closed by the spring loading. Under these conditions both pumps5 and 6 will be delivering their full capacity tothe control unit 9.

As the aircraft climbs the amount of fuel supplied to the engine it}will fall and the fuel flow in the by-pass conduit 11 will increase.This flow passing through the orifice 12a of theflow responsive valve 12will give rise to a pressure drop across said orifice 12a and when thispressure drop reaches a predetermined value the sleeve 12c will moveagainst the load of the spring 1% and start to close the port 19. Thisclosing of the port 19 causes the pressure in the servo cylinder 17 toincrease to approach the value of the pressure in the bypass conduit 11to which it is connected by the orifice 18.

This pressure in the cylinder 17 will overcome the spring load on thepiston and start to open the valve 14.

As the fuel requirements of the engine continue to decrease the flow inthe bypass conduit will remain sub stantially constant while the excessfuel is by-passed through the servo operated valve 14 the pump 5continuing to deliver proportion of its output through the nonreturnvalve "7 to the control unit 9. This action will continue until theentire delivery of the pump 5 is being by-passed through the servooperated valve 14. A slight increase in flow in the by-pass conduit 11will now cause the flow sensitive valve 12 to close the servo bleed port19 completely. This will cause the servo operated valve to move rapidlyto its fully open position and the pump 5 will now be circulating fuelat virtually zero pressure and the non-return valve 7 will be closed. itthe engines fuel requirements continue to decrease the flow through theby-pass conduit 11 will again increase and will cause the sleeve 12c ofthe flow sensitive valve to move back and allow the excess flow to passthrough the low pressure connection 11a thus avoiding an increase ofpressure through the orifice 12s.

Under these conditions the power input to the pumps 5 and 6 is reducedby-one half with a consequent reduction in temperature rise comparedwith that which would occur if both pumps were operating at pressure.Under these conditions the power input to the pumps 5 and 6 is reducedby one half with a consequent reduction in temperature rise comparedwith that which would occur if both pumps were operating at pressure.

Referring to Fig. 2, the liquid fuel is supplied from a tank 21, by wayof a conduit 22 communicating with three passages 23, 24, 25, arrangedin parallel. Each passage 23, 24, 25 contains a gear pump 26, 27, 28 forsupplying pressurised liquid fuel through non-return 24 of the pump 27and a similar conduit 37 is connected to the delivery conduit 25 of thepump 28, both conduits 24, 25 being provided with servo-operatedthrottle-valves 38, 39 operated by hydraulic means consisting of acylinder and piston arrangement 40, 41, passages 42 and 43 and conduits44, 45 having an orifice 46, 47 located in each said conduit.

, In operation, excess liquid fuel from the control unit 32 will movethe flow responsive valve 35 to close the passage 42, thereby causingpressure to increase in servovalve cylinder 40. This has the effect ofopening servov alve 38 and thereby causing fuel from the second pump 27to be circulated back to the low pressure inlet 22 through the conduit36, whereby the pump 27 is unloaded. Should the flow in the bypass 34 besufficient to move the pressure responsive valve 35 further, therebyclosing passage 43, itwillcause a build up of pressure in the cylinder41 which will open the valve 39 whereby the third pump 28 is unloaded,the system being maintained by the first pump 26.

. The operation of the flow responsive valve 35 is similar to thatherein described with reference to Fig. l with the exception that thepumps 27, 23 are operated in sequence and like reference numerals inFig. 1 apply equally to those applied to the flow responsive valve 35. Afurther advantage of this system is the additional safety factor, for ifa pump should fail, the others will automatically take over. One pump issufficient to maintain full power at altitude.

The system described for two and three pumps can be adapted to cover anynumber of stages.

I claim:

1. In a fluid control system, a fuel supply, first and second positivedisplacement pumps arranged in parallel and connected to said supply, afuel system delivery connected to the outlet from said first and secondpumps receiving fuel under pressure individually discharged by saidpumps, a control unit metering the correct flow of fuel in said deliveryand which is of the type that bypasses the excess fuel which is receivedby the same, a by-pass passage leading from said control unit to saidsupply returning such excess fuel from said control unit to the fuelsupply, a branch passage leading from the outlet of the second pump andcommunicating with the fuel supply, a spring loaded servo-operated valvemeans arranged in said branch passage, a further passage ineludingmetering means for applying fuel from the bypass passage'to operate theservo-operated valve in opposition to its return spring loading, asingle flow responsive valve means arranged in said by-pass passagebeyond said further passage and a separate passage-way controlled bysaid flow-responsive valve means connecting the servo-operated valvemeans with the fuel supply in a manner such that increased flow in saidby-pass passage causes an opening movement of the servo-operated valve.

2. In a fluid control system, a fuel supply, a first positivedisplacement pump and at least two further positive displacement pumpseach having an inlet and an outlet, the inlets of all said pumps beingconnected in parallel to said supply, a fuel delivery system connectedto the outlets of all said pumps in parallel to receive fuel underpressure individually discharged by said pumps, a control unit meteringthe correct flow of fuel in saidvdelivery', a

by-pass passage leading from said controiunit tothe fuel supply, saidunit being of the type that by-passes the excess fuel which is receivedby the same, a plurality of branch passages respectively leading fromthe outlet of:

each such further pump and communicating with the fuel supply, aplurality of individual spring-loaded servooperated valve meansrespectively arranged in each such branch passage and respectivelycontrolling the return flow of fuel to the supply through said branchpassage,'a plurality of further passages, each including metering means,for applying fuel from the by-pass passage to respectively operate eachservo-operated valve means in opposition to the spring loading of suchvalve means; a single flow-responsive valve means arranged in saidby-pass passage beyond said further passages, and a plu'. rality ofseparate passageways controlled by the single flow-responsive valvemeans and respectively connecting each of said individual servo-operatedvalve means with thefuel supply in such manner that progressively inecreased flow in said by-pass passage causes sequential closing of saidseparate passageways resulting in. se quential opening movements of saidindividual servo= operated valve means according to the increasingpressure of fluid in the by-pass passage.

References Cited in the file of this patent Carey Mar. 13, 1956

